Fat Measurements Are Valuable
A measurement of the amount of fat in a human's body can be valuable and useful for many reasons. First, fat measurements can be a valuable aid in monitoring body tone. Further, they provide a means for monitoring and indicating the progress of a weight-loss or exercise program. An indication of a quantitative progression can be very valuable psychologically to the exerciser or reducer as a means of encouraging continued participation. Still further, when a person embarks on an exercise program, he or she will usually gain weight by virtue of added muscle mass. Thus the person may erroneously believe he or she is becoming "fatter", when in fact the ratio of fat to lean body tissue is actually declining. Measurements of the ratio of fat to lean tissue will correct this misinformation.
Prior-Art Fat-To-Lean Measurement Techniques Left Much To Be Desired
The ratio of fat to lean tissue in an animal's or in an inanimate body of tissue (such as a piece of meat, for example) can be measured in a number of ways. In one way, the ratio is determined with the aid of direct weighing and volume-determining apparatus using any of several techniques.
In one weight-volume method, the tissues are subjected to electromagnetic radiation. The electrical impedance characteristic of pure lean tissue which contains minimal fat is measured and recorded. The properties of a pure sample of fat are also measured and recorded. Then the tissue of interest is studied using the same method. The relative amounts of lean tissue and fat contained in the sample are determined by interpolation of the data (e.g., electrical impedance) between the known properties for pure fat and pure lean tissue.
A second class of measurements involves the determination of the volume of the subject. Once this is known, the subject is weighed and its density calculated. Again, the ratio of fat to lean tissue is determined by interpolation of the data between the two known densities for pure fat and pure lean tissue.
Harker, in U.S. Pat. No. 3,735,247, 1973, employs an electronic system to measure the "fat-to-lean" ratio of tissue, either in vitro or in vivo. His apparatus consists of electronic circuitry which uses non-contact means to measure the resistivity and dielectric constant of the tissue. An oscillator applies an alternating current signal to a solenoidal coil. The electromagnetic field thus produced is coupled to the tissue of interest. Generally, this is done by placing the tissue or animal inside a coil of appropriate size. Harker's circuitry then measures the impedance change in the coil brought about by insertion of the animal into the coil. The complex impedance of the animal tissue thus measured can be expressed in terms of real and imaginary components using variables well understood by those familiar with alternating-current electronic circuitry. These components in turn are used to determine the resistivity and dielectric constant of the sample tissue. Knowing the impedance of fat and lean tissue, it is possible by interpolation to infer the intermediate, relative amounts of fat and lean tissues contained within the volume of the coil.
While Harker's system provides information about the relative amounts of fat and lean tissue in a subject, it has a number of practical disadvantages. First, the determination of the ratio of fat to lean tissue is indirect. Using Harker's method, this ratio is determined by interpolation of the data between two known values: one for lean tissue, and the other for fat. Errors in the measurement technique could arise from non-linearities in the relationship between the impedance and the fat-to-lean ratio. Further, it is possible that fat distributed uniformly throughout the tissue would yield a different reading than fat lumped together at one location, especially if that location were near one end of the solenoidal coil where the electromagnetic field is divergent. Further, the requirement that the subject be placed inside a solenoidal coil could require a coil of substantial size, e.g. in the study of tissue in a human being. Thus Harker's system would not be suitable for home use. Still further, errors could result if the subject moves while the impedance is being measured.
Vogelman, in U.S. Pat. No. 4,144,763, 1979, employs two chambers to determine the density of an animal or human being. The chambers are coupled together by a connecting pipe and valves. His method consists of pressurizing the first chamber above atmospheric pressure and measuring the pressure in this chamber. The object to be measured is placed in the second chamber, which can be maintained at atmospheric pressure. Both chambers are then sealed from the outside environment. A valve in the pipe connecting the first and second chambers is then opened and the equalized pressure of the two chambers is measured. Using Boyle's law, the initial and final pressures may be used to calculate the volume of the body within the second chamber. The subject is then weighed and its density determined. Further calculations using empirical equations are then used to determine the percentage of body fat in the measured object.
Vogelman's method, like Harker's, also suffers from the requirement that the chambers be sufficiently large to contain the subject. In the study of human beings, the chambers will of necessity be large and relatively expensive, especially since they must be sealed against air leaks. Further, temperature changes during the measurement cycle or a temperature gradient between the two chambers could result in a false reading.
Brachet, in U.S. Pat. No. 4,184,371, 1980, describes an apparatus for measuring the density of a body. Brachet's apparatus comprises two chambers: one to receive the body, the other an auxiliary chamber. A subsonic wave generator, typically operating at 5 Hz, applies subsonic pressure waves to both chambers. A differential manometer is connected between the chambers and means are provided for equalizing the subsonic pressures of the chambers. Measurement means are driven by the mechanism for equalizing the above-mentioned subsonic pressures. Finally a scale in the first chamber weighs the body.
Although the weight of the body is obtained directly, using an ordinary scale, the body's volume must be obtained using volumetric pressure variations between the chamber containing the body and the reference chamber. This is accomplished by zeroing the commutating, differential manometer and noting the readings of the measurement means coupled to the mechanism which equalizes the pressures between the two chambers. A set of equations is then employed to give the volume and, knowing the weight, the density of the body.
Brachet's apparatus shares one impracticality with Vogelman's and Harker's: the volume of the chamber required for human study, for example, is very large. Further, an animal subject is unlikely to stand still during a measurement. This adversely affects the weight determination by introducing errors into the measurement.
Prior-Art Mass Determination Fat Measurement Methods Also Have Drawbacks
Other related prior-art fat measurement methods include the determination of mass by various means.
Storace, in U.S. Pat. No. 4,050,530, 1977, teaches a method and an apparatus for weighing or determining the mass of an object. A first table is supported above a floor or fixed reference surface by piezoelectric crystals. When an appropriate electrical signal is applied to the piezoelectric crystals, the table will vibrate. A second table is supported above the first by a second set of piezoelectric crystals. The second set of crystals couples the two tables together mechanically. The second table contains a "pan" which holds the object to be weighed.
An oscillating voltage is applied to the first set of piezoelectric crystals, i.e., the ones which support the first table above the floor or reference surface. By virtue of the mechanical coupling, the second set of piezoelectric crystals will vibrate at the same frequency as the first set. The amplitude of the signal voltage output from the second set of crystals is a function of the mass and/or supported weight in the pan. In practice, the oscillating voltage obtained from the second set of piezoelectric crystals, i.e., those which support the pan, is rectified. Thus, a steady direct-current voltage is obtained which is representative of the mass or weight in the pan.
Barry et al., in U.S. Pat. No. 4,429,574, 1984, describe a system containing apparatus and circuitry for measuring the mass and weight of a sample. Their system employs an electromechanical mass-spring cell assembly. The cell applies an oscillatory motion to the subject whose mass or weight is to be determined. Electronics associated with the cell maintains a resonant frequency oscillation in the system consisting of the subject and the electromechanical assembly. The mechanical resonant frequency of the system is a function of the mass of the sample. The sample's mass and the acceleration due to gravity can be used to determine the sample's weight.
Storace and Barry both assume that the subject is a simple mass which moves as a unit. Both systems will be subject to error if the subject's mass is composed of two or more loosely connected parts. These parts and the connection between them will have one or more mechanical resonance frequencies of their own. A beat frequency will result from the mixing of multiple resonant frequencies. It is possible that the amplitude of the beat note will be great enough to completely obscure the mass reading obtained. Similarly, if the subject moves during a measurement, errors will be indicated.
Further, both of these methods rely on the application of a mechanical perturbation to the subject. This can be undesirable if the subject is sensitive to the vibrations necessary to produce a reading.
Disadvantages Of Prior-Art Fat Determination By Weighing Techniques
A number of weighing techniques are also employed as an adjunct to fat-determining measurements.
Neumann et al., in U.S. Pat. No. 4,008,405, 1977, is concerned with the prevention of weighing errors caused by motion of the mass being weighed. Electronic circuitry is employed to sense variation in the apparent weight over some time period. The readout of the electronic scale is blanked until the motion-induced variability in the apparent weight is reduced below a threshold value. When the measured weight reaches a steady value, the electronic scale's readout display is activated.
Yano et al., in U.S. Pat. No. 4,347,903, 1982, describe an electronic weighing balance which ascribes an average weight to a body which tends to move while it is being weighed. An analog signal representative of the apparent weight on the balance is converted to a digital representation of this signal using analog-to-digital converter in well-known fashion. The subject to be weighed is placed in the pan of the scale. The apparent weight of the subject is measured periodically. An algorithm is used which optimizes the timing of the taking and storing of samples of the subject's apparent weight in order to minimize error in the final result. These samples are then averaged to yield the subject's actual weight.
Feinland et al., in U.S. Pat. No. 4,412,298, 1983, teach a method for tracking creep and drift of a digital scale after a load has been placed on the scale's pan. Electronic means employing an analog signal derived from the weight in the pan, and an analog-to-digital converter are used to obtain a digital representation of the weight being measured. A microprocessor circuit is employed to store the continuously updated tare weight just prior to weighing. After a load is placed on the pan and the balance has come to equilibrium, the creep and drift are continuously monitored. The tare weight is adjusted for the creep and drift. The storing of the adjusted tare weight results in a constant net weight being obtained.
Neumann et al and Yano et al eliminate errors caused by motion of the subject. Feinland et al eliminate errors due to creep and drift caused by a heavy weight. These methods strive to perfect measurement of the weight of the subject under varying conditions. None of these methods directly addresses the measurement of fat v. lean tissue.